Power steering reservoir and cooler

ABSTRACT

A combined power steering hydraulic fluid reservoir and cooling unit (12, 112) includes a housing (14, 114) having a reservoir tank (16, 116) for receiving and collecting hydraulic fluid from a power steering gear (18) and holding the hydraulic fluid in readiness for supply to a hydraulic pump (20). The housing has a heat exchanger (22, 122) with a cooling liquid flow path therethrough in heat transfer relation with the hydraulic fluid, eliminating a hydraulic fluid cooler otherwise connected in series between the power steering gear and the reservoir tank, and eliminating two extra hose connections therefor.

CROSS REFERENCE TO RELATED APPLICATION

This application is a division of U.S. application Ser. No. 09/108,056,filed Jun. 30, 1998.

BACKGROUND AND SUMMARY OF THE INVENTION

The invention relates to power steering reservoirs, particularly onheavy duty trucks and busses, and the need to dissipate heat within thesystem, in reduced space and with lower cost.

One function of power steering reservoirs on heavy duty trucks andbusses is to dissipate heat generated within the system. A largerreservoir is used when additional cooling is required. In some cases, ahydraulic fluid cooler is also required to reduce the operatingtemperature to an acceptable level. The hydraulic fluid cooling deviceis typically connected to the return hose between the power steeringgear and the reservoir, i.e. a series connection with two additionalhose connections.

Truck manufacturers have expressed a need for reducing systemtemperatures. High operating temperatures cause seals, hoses, andhydraulic fluid to break down and wear out more quickly. A standard offthe shelf hydraulic oil cooler will significantly reduce systemtemperatures. However, the added cost and installation time isobjectionable.

Truck aerodynamic improvements are limiting the amount of air flowthrough the engine compartment. This reduction in air flow also reducethe cooling efficiency of the power steering reservoir. Sloping fronthoods are reducing under hood space, which makes larger reservoirsimpractical.

The present invention addresses and solves the above-noted need in aparticularly simple and cost effective manner. The invention enableselimination of a hydraulic cooler otherwise connected in series betweenthe power steering gear and the reservoir, and eliminates the two extrahose connections therefor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a power steering systemincorporating the present invention.

FIG. 2 is a side view partially in section of a combined power steeringhydraulic fluid reservoir and cooling unit constructed in accordancewith the invention.

FIG. 3 is a sectional view taken along line 3--3 of FIG. 2.

FIG. 4 is a sectional view of a portion of the structure of FIG. 2.

FIG. 5 is a sectional view taken along line 5--5 of FIG. 4.

FIG. 6 is a view like FIG. 1 and shows a further embodiment.

FIG. 7 is a view like FIG. 2 and shows a further embodiment.

FIG. 8 is a sectional view taken along line 8--8 of FIG. 7.

FIG. 9 is a sectional view taken along line 9--9 of FIG. 7.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a combined power steering hydraulic fluid reservoir andcooling unit 12 including a housing 14 having a reservoir tank 16 forreceiving and collecting hydraulic fluid from a power steering gear 18and holding the hydraulic fluid in readiness for supply to a hydraulicpump 20. The housing has a heat exchanger 22 with a cooling liquid flowpath therethrough in heat transfer relation with the hydraulic fluid,eliminating a hydraulic fluid cooler otherwise connected in seriesbetween power steering gear 18 and tank 16, and eliminating the twoextra hose connections therefor. Housing 14 has a first hose connection24 providing a hydraulic fluid inlet, a second hose connection 26providing a hydraulic fluid outlet, a third hose connection 28 providinga cooling liquid inlet, and a fourth hose connection 30 providing acooling liquid outlet. The housing may include a further hydraulic fluidinlet 32 as a bypass receiving excess flow from pump 20.

FIG. 2 shows reservoir tank 14, which is Nelson Industries Part No.94131A, modified in accordance with the present invention. The tank is acylindrical canister extending axially along a vertical axis 34 betweendistally opposite lower and upper axial ends 36 and 38. Extendingthrough lower axial end 36 is heat exchanger 22, provided by a SerckPart No. 31002-97-AA01. Heat exchanger 22 extends axially along axis 34through axial end 36 of reservoir tank 16. The cooling liquid flow paththrough heat exchanger 22 is in heat transfer relation with hydraulicfluid in tank 16.

Heat exchanger 22 has a side wall 40 extending axially between distallyopposite lower and upper end walls 42 and 44. Cooling liquid inlet 28and cooling liquid outlet 30 both extend axially through lower end wall42. Hydraulic fluid inlet 24 extends radially through side wall 40. Sidewall 40 of heat exchanger 22 extends axially through lower axial end 36of reservoir tank 16. Side wall 40 of heat exchanger 22 has a firstportion 46 exterior to reservoir tank 16, and a second portion 48interior to reservoir tank 16. Hydraulic fluid inlet 24 extends radiallythrough first portion 46 of side wall 40. Second portion 48 of side wall40 has a pair of openings 50, 52, FIGS. 2, 4 and 5, therethrough passinghydraulic fluid into lower portion 54 of tank 16 below divider wall 55.

Coolant liquid flows from heat exchanger inlet 28 into lower entryplenum 56, FIG. 4, then upwardly through a plurality of transfer tubes58 to upper plenum 60 then downwardly through a plurality of transfertubes 62 to lower exit plenum 64 then to cooling liquid outlet 30.Entrance and exit plenums 56 and 64 are separated by dividing wall 66.Hydraulic fluid flows from hydraulic fluid inlet 24 into heat exchanger22 and is directed around tubes 62, 58 in a tortuous flow path 68 bydirectional divider walls 70, 72, and then flows through openings 50, 52into lower portion 54 of tank 16. The hydraulic fluid then flowsupwardly as shown at arrow 74, FIG. 2, through central standpipe 76 andthen radially outwardly through openings such as 78 therein, and thenthrough filter 80 to hydraulic fluid outlet 26. If filter 80 becomesclogged, or the pressure drop thereacross otherwise exceeds a giventhreshold, the pressure build-up compresses bypass spring 82 axiallyupwardly to permit hydraulic fluid to bypass the filter as shown at flowarrow 84, as is known. Dipstick 86 in the housing permits checking offluid level. A pair of mounting bands or straps 88, 90 extend around thehousing and have ends such as 92, 94, FIG. 3, mountable to a verticalsurface in the engine compartment, such as a fire wall, etc., andtightenable by a bolt 96.

FIG. 6 is like FIG. 1 and shows a further embodiment of a combined powersteering hydraulic fluid reservoir and cooling unit 112 including ahousing 114 having a reservoir tank 116 for receiving and collectinghydraulic fluid from power steering gear 18 and holding the hydraulicfluid in readiness for supply to hydraulic pump 20. The tank is providedby a cylindrical canister extending axially along vertical axis 34. Thehousing has a heat exchanger 122 with a cooling liquid flow paththerethrough in heat transfer relation with the hydraulic fluid in tank116. The heat exchanger is provided by an annular jacket around thecanister. The jacket has upper and lower axially spaced annular chambers124 and 126 separated by a circumferential divider wall or baffle 128therebetween.

Annular chamber 124 has a cooling liquid inlet 130, and annular chamber126 has a cooling liquid outlet 132. Baffle 128 has a transfer passage134 therethrough, FIGS. 6-9, such that the cooling liquid flow path isthrough cooling liquid inlet 130, then through annular chamber 124, thenthrough transfer passage 134, then through annular chamber 126, thenthrough cooling liquid outlet 132. The hydraulic fluid flow path is fromhydraulic fluid inlet 136, FIGS. 6, 7, then upwardly through centralstandpipe 138, then radially outwardly through apertures 140 thenthrough filter 142 against the side wall of tank 116, then to hydraulicfluid outlet 144. Bypass inlet 146 to the tank is provided for receivingexcess flow from pump 20. If filter 142 becomes clogged, or the pressuredrop thereacross otherwise exceeds a given threshold, such pressurebuild-up compresses bypass spring 148 axially upwardly to enablehydraulic fluid flow to bypass filter 142, as above described. Dipstick150 enables checking of hydraulic fluid level. A pair of mounting bandsor straps 152, 154 extend around jacket 122 and have ends such as 156,158, FIGS. 8 and 9, mountable to a vertical surface in the enginecompartment such as a fire wall, etc., and tightenable by a bolt 160.

Baffle 128 is C-shaped in radial cross section as shown at 162 in FIG.8. The facing ends 164 and 166 of the C-shape 162 define transferpassage 134 in the circumferential arcuate gap 166 therebetween.Transfer passage 134 extends axially along canister 116 between annularchambers 124 and 126. Jacket 122 is an annular sleeve having a side wall168 spaced radially outwardly of canister 116 to define an annular spacetherebetween. Baffle 128 is provided by a recessed groove formed in sidewall 168 of the sleeve and extending radially inwardly towards side wall170 of the canister. The groove extends partially circumferentiallyaround the canister and divides the annular space into the noted annularchambers 124 and 126 and provides the noted C-shaped baffletherebetween. Cooling liquid inlet 130 and cooling liquid outlet 132 arediametrically opposite gap 166 between facing ends 162 and 164 of theC-shape 162. Baffle groove 128 is V-shaped in axial cross-section, FIG.7, with the apex 172 of the V engaging tank 116 at side wall 170.

As above noted, transfer passage 134 through baffle 128 is diametricallyopposite cooling liquid inlet 130 along the circumference of cylindricalcanister 116 such that cooling liquid from cooling liquid inlet 130splits into two paths in annular chamber 124, a path 174, FIG. 8,traversing 180° in a semi-circle to transfer passage 134, and a path 176traversing oppositely from first path 174 and 180° in a semi-circle totransfer passage 134, such that cooling liquid from cooling liquid inlet130 splits into two paths 174, 176 and then rejoins at transfer passage134. Transfer passage 134 is diametrically opposite cooling liquidoutlet 132 along the circumference of cylindrical canister 116 such thatcooling liquid from transfer passage 134 splits into two paths inannular chamber 126, a path traversing 180° in a semi-circle to coolingliquid outlet 132, and another path traversing oppositely and 180° in asemi-circle to cooling liquid outlet 132, such that cooling liquid fromtransfer passage 134 splits into two paths and then rejoins at coolingliquid outlet 132.

Hydraulic fluid flows radially outwardly through filter 142 and againstside wall portion 170 of canister 116. Jacket 122 is around portion 170of the side wall of the canister and provides the noted cooling chamberthereat. Hydraulic fluid exiting from filter 142 flows against cooledportion 170 of the side wall of the canister and gives up heat tocooling liquid in cooling chambers 124, 126 provided by jacket 122, suchthat hydraulic fluid is filtered first and cooled second. This ispreferred because there is then less pressure drop at the coolinginterface, and because filtering of hot fluid reduces the chance ofbypass spring 148 opening.

It is recognized that various equivalents, alternatives andmodifications are possible within the scope of the appended claims.

I claim:
 1. A combined power steering hydraulic fluid reservoir andcooling unit comprising a housing having a reservoir tank for receivingand collecting hydraulic fluid from a power steering gear and holdingsaid hydraulic fluid in readiness for supply to a hydraulic pump, saidreservoir tank comprising a cylindrical canister extending axially alongan axis between distally opposite axial ends, said housing having a heatexchanger with a cooling liquid flow path therethrough in heat transferrelation with said hydraulic fluid, said heat exchanger extendingaxially through one of said axial ends of said reservoir tank, saidreservoir tank having a hydraulic fluid outlet, said heat exchangerhaving a hydraulic fluid inlet and a cooling liquid inlet and a coolingliquid outlet.
 2. The unit according to claim 1 wherein said heatexchanger extends axially along an axis and has a side wall extendingaxially between distally opposite end walls, said cooling liquid inletand said cooling liquid outlet both extend axially through one of saidend walls of said heat exchanger, said hydraulic fluid inlet extendsradially through said side wall of said heat exchanger.
 3. The unitaccording to claim 2 wherein said side wall of said heat exchangerextends axially through said one axial end of said reservoir tank, saidside wall of said heat exchanger has a first portion exterior to saidreservoir tank, and a second portion interior to said reservoir tank,said hydraulic fluid inlet extending radially through said first portionof said side wall of said heat exchanger, said second portion of saidside wall of said heat exchanger having one or more openingstherethrough passing hydraulic fluid into said reservoir tank.
 4. Theunit according to claim 2 wherein said axis of said canister and saidaxis of said heat exchanger are coincident.